WASHINGTON - More than one of every 100 adults in the United States is either in jail or prison, said a study released Thursday.

The study, conducted by the Pew Center on the States' Public Safety Performance Project, found that at the beginning of 2008, 2,319,258 adults -- or one in every 99.1 men and women -- were incarcerated in U.S. prisons or jails.

During 2007, the study found that the U.S. prison population rose by more than 25,000 inmates, creating a budget strain on many state governments. The rising prison population followed adoption of tougher state and federal sentencing beginning in the 1980s.

States spent more than $49 billion on corrections in 2007, up from $11 billion 20 years before. Even with the added investments in corrections, the national recidivism rate remains virtually unchanged, researchers said.

The study found that about half of released inmates return to custody within three years.

"For all the money spent on corrections today, there hasn't been a clear and convincing return for public safety," said Adam Gelb, director of the Public Safety Performance Project. "More and more states are beginning to rethink their reliance on prisons for lower-level offenders and finding strategies that are tough on crime without being so tough on taxpayers."